ナトリウムの高圧変化から星や惑星の内部がわかる(Sodium’s high-pressure transformation can tell us about the interiors of stars, planets)

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2023-12-28 バッファロー大学(UB)

◆バッファロー大学主導の研究では、高圧下で金属が絶縁体に変化する現象の背後にある化学結合が解明された。ナトリウムが強い圧力で透明な絶縁体に変わる仕組みが、従来の仮説を裏付け、理論的な予測を発展させた。
◆これにより、星や惑星の内部、磁場生成、進化などに関する大きな疑問に対する洞察が得られ、高圧下での他の物質の振る舞いを予測する手法が示唆された。研究は高圧下での物質変化を探る新たな理論の進展を示している。

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Na-hP4のエレクトライド性について On the Electride Nature of Na-hP4

Stefano Racioppi, Christian V. Storm, Malcolm I. McMahon, Eva Zurek
Angewandte Chemie International Edition  Published: 05 October 2023
DOI:https://doi.org/10.1002/anie.202310802

Graphical Abstract

The Na-hP4 phase, a high pressure electride, contains clusters of eleven sodium atoms within which charge is localized. Quantum chemical calculations show that this build-up of interstitial charge stems from the overlap of pd hybrid orbitals on the sodium atoms comprising this cluster, resulting in the formation of a multicentered bond, increased density, and semiconducting behavior.

ナトリウムの高圧変化から星や惑星の内部がわかる(Sodium’s high-pressure transformation can tell us about the interiors of stars, planets)

Abstract

Early quantum mechanical models suggested that pressure drives solids towards free-electron metal behavior where the ions are locked into simple close-packed structures. The prediction and subsequent discovery of high-pressure electrides (HPEs), compounds assuming open structures where the valence electrons are localized in interstitial voids, required a paradigm shift. Our quantum chemical calculations on the iconic insulating Na-hP4 HPE show that increasing density causes a 3s→3pd electronic transition due to Pauli repulsion between the 1s2s and 3s states, and orthogonality of the 3pd states to the core. The large lobes of the resulting Na-pd hybrid orbitals point towards the center of an 11-membered penta-capped trigonal prism and overlap constructively, forming multicentered bonds, which are responsible for the emergence of the interstitial charge localization in Na-hP4. These multicentered bonds facilitate the increased density of this phase, which is key for its stabilization under pressure.

1700応用理学一般
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